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In the Bitcoin Era, Ransomware Attacks Surge

Digital currency, better software help hackers hold data hostage

Dave Winston, crew chief with Circle Sport-Leavine Family Racing, fell victim to a ransomware attack. What are these attacks and how can they be stopped? Photo: Joe Chisholm for Circle Sport-Leavine Family Racing

One evening in April, Dave Winston stood in a convenience store in suburban Charlotte, N.C., uneasily shoving $20 bills into a slim automated-teller machine unlike any he had ever seen. He was buying bitcoin, a digital currency unknown to him a few hours earlier, before hackers took over his computer.

Mr. Winston, crew chief with the Circle Sport-Leavine Family Nascar race team, is among a growing number of victims of a pernicious...